The frequency spectrum used by a particular communication system may be licensed or unlicensed. Licensed frequency spectrum (frequency band) is licensed to a system operator by a government agency such as the Federal Communications Commission (FCC). An example of such licensed spectrum includes frequency bands used for cellular communication. An unlicensed frequency band is any portion of frequency spectrum that does not require a license from the government agency to communicate with the unlicensed frequency band. Equipment operating within the unlicensed band, however, typically must adhere to regulations and/or communication standards. An example of unlicensed frequency spectrum includes frequency bands used for Institute of Electrical and Electronics Engineers (IEEE) 802.11 communication.
In some communication system implementations, a base station, such as eNodeB, provides a primary cell (PCell) and a secondary cell (SCell) where the two cells use different frequencies. In some situations, the PCell may use a licensed frequency band and the SCell operates in an unlicensed frequency band.